1. Technical Field
The invention relates generally to light steering, and particularly to methods and devices for reducing the physical size of light steering devices.
2. Description of Related Art
In optical communication systems, especially on-chip integrated systems, it is desirable to miniaturize the light steering devices. Currently such devices are physically considerably larger than λ, the wavelength of the steered radiation (light). The fundamental physics of conventional lenses, which create images by capturing propagating light waves reflected by objects and then bending them, limit them to a resolution on the order of λ due to the so called diffraction limit. The angle of the bend is determined by the index of refraction and is always positive in common lenses. However, objects also emit “evanescent” waves that carry a great deal of detail (specifically, about object features on a sub-wavelength scale <λ) but are far more elusive because they decay exponentially away from the source and thus never reach the image plane of a lens, and this leads to the diffraction limit.
The recent advent of artificial structures with electromagnetic resonances has enabled the development of negative index metamaterials (NIMs). NIMs are materials for which both the electric permittivity E and the magnetic permeability μ are simultaneously negative (ε<0, μ<0). Such materials have not been found to exist in nature, but can now be fabricated by combining artificially magnetic structures with artificial electric structures. Because the refractive index N of these materials is positive, they are in fact transparent to light and, by being formed with a structure on the order of λ or smaller, can be used for near-field “superlensing”—that is, focusing features much smaller than the wavelength λ of the light that they are focusing.
Recently, it has been shown that dielectric photonic crystals (PhCs) also can possess negative refraction. Photonic crystals are periodic optical nanostructures composed of periodic dielectric or metallo-dielectric nanostructures that are designed to affect the propagation of electromagnetic waves (EM) by defining allowed and forbidden electronic energy bands (forming so-called photonic band gaps when the unit cell size is comparable to integers of the EM wavelength in the material) and giving rise to certain desirable optical phenomena including inhibition of spontaneous emission, high-reflecting omni-directional mirrors (such as Bragg mirrors) and low-loss-waveguiding. Because of necessarily strong variation of optical index in the unit cell (in other words, strong spatial dispersion) some PhCs exhibit negative refraction which is a very strong effect, with experiments having shown that the incident light angle between the normal to the surface of a PhC can be as small as 7° while the angle of refraction can be as large as 70°. It has also been demonstrated that a slab of PhC may enable an effective free space transmission of light between fibers with separation comparable to λ.
The present writing addresses the need for reducing the size of light steering devices by utilizing the superlensing optical properties of NIM PhCs.